Building career decision self-efficacy (CDSE) and engaging in career exploratory behavior (CEB) have been identified as key adaptive career behaviors that promote successful career choice and development among adolescents and young adults. Using the RI-CLPM and a five-wave dataset gathered from first-year exploratory college students (N = 833), this study examined temporal predominance between CDSE and CEB and their effects in mediating the relations of personality traits to career decidedness. At the within-person level, the bidirectional model revealed a reciprocal relation from T2 CDSE to T5 CEB for the entire sample. A similar temporal pattern also emerged for European American students and female students, whereas the baseline model was retained for male students and students of color. At the between-person level, random intercepts of CDSE and CEB were found to mediate the relations of T1 extraversion and emotional stability to T5 career decidedness for the entire sample. While the mediating effect of CDSE was significant and tended to be larger than that of CEB across racial/ethnic and gender subgroupings, mediational pathways of personality traits → CEB → career decidedness varied by race/ethnicity. This study provides evidence for theory-based hypotheses regarding how CDSE and CEB relate to each other temporally within the student and how the two variables channel the effects of personality traits on career decidedness between students. It also offers practical implications for including CDSE and CEB in career interventions designed to facilitate career development of exploratory students of different racial/ethnic and gender backgrounds during their initial transition to college.